A Gc predictor. This predicts a time based on measuring rates,
which are reported to the given estimator. Rates are measured
every period. The estimated GC time is based on interpolating
the rate estimated by estimator.

Unix-like load average, an exponentially weighted moving average,
smoothed to the given interval (counted in number of
measurements).

Unix-like load average, an exponentially weighted moving average,
smoothed to the given interval (counted in number of
measurements).
See: http://web.mit.edu/saltzer/www/publications/instrumentation.html